what you can do is name a few of them (algebraically, you can list the rule to generate them all, but we won't worry about that right now)
So what you do is hit 2nd, then trace. Then you hit either "minimum" or "maximum" depending on whether you want the min or max point.
The first point after x = 0 is a max, so pick 4: maximum
Then set up the left and right bounds to the left and right of the max point. Then make the best guess you can and hit enter

if that's the case (as satellite73 is saying), then you would just type in arcsin(2/5) or sin^-1(2/5) to get roughly 23.578 degrees
Keep in mind that 180 - 23.578 = 156.422 degrees is also a solution (assuming you're restricted from 0 to 360 degrees)

okay this is EXACTLY the right answer so ok for this part sin(x) = 2/5 <--- I see how you got this now
x = arcsin(2/5)
x = 0.4115 or x = pi - 0.4115
x = 0.4115 or x = 2.7301
what did u do on the calculator to get these 2 critical points???

Keep in mind that sin^-1 or arcsine is a function, so it's only going to spit out one answer. However, there are 2 solutions to sin(x) = 2/5 where 0 < x < pi as Dido525 is saying
So that's why I'm subtracting that first result from pi.

If the sine of some angle is positive, then we're only focusing on the upper half (since the positive y coordinates point to a positive sine value)
There are 2 ways to generate a triangle in which the sine of the reference angle is 2/5 and they look like this
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